Variable track length photocopier lens system

ABSTRACT

An optical lens system comprises a symmetrical anastigmatic lens unit in combination with a two-element variable-power unit which permits variation in the total distances between the object and image planes with maintained aberration correction.

United States Patent,

Inventors Peter Arnold Merigold Prestatyn, Flintshire; Philip .1. Rogers, Meliden, Flintshire, both of liorth Wales Appl. No. 825,209

Filed May 16, 1969' Patented Sept. 14, 1971 Assignee Pilkington Perkin-Elmer Limited Liverpool, England Priority May 21, 1968 Great Britain 24206/68 VARIABLE TRACK LENGTH PHOTOCOPIER LENS SYSTEM 2 Claims, 1 Drawing Fig.

us. Cl 350/216, 350 227, 350/255 Int. Cl G021) 7/04, G02b 9/26, G02b 9/60 [50] Field oiSearch 350/216, 215, 221, 226, 227

[56] References Cited UNITED STATES PATENTS 3,202,051 8/1965 Bechtold 350/226 3,301,130 1/1967 Buchroeder et a1. 350/227 3,370,904 2/1968 Hudson 350/221 X 3,436,145 4/1969 Bechtold 350/215 Primary Examiner-John K. Corbin Att0rneyMattern, Ware and Davis ABSTRACT: An optical lens system comprises a symmetrical anastigmatic lens unit in combination with a two-element variable-power unit which permits variation in the total distances between the object and image planes with maintained aberration correction.

VAlRlAlilvLlE TRACK LENGTH lPll'liOTOCOlPllER LENS SYSTEM BACKGROUND OF THE INVENTION This invention relates to optical lens systems, and is particularly, but not exclusively, applicable to lens systems for use in document-copying apparatus.

When fitting ll lens system to an apparatus such as a document copier in which it is to be used, it is desirable that the mini distance between the object and image planes of the system have a predetermined value to close limits of tolerance. To obtain such close limits with a lens system produced in quantity would generally prove difficult and expensive.

An object of this invention is to provide a system which permits of variation or adjustment of the total distance between the object and image planes.

SUMMARY The present invention provides an optical lens system comprising a symmetrical anastigmatic lens unit in combination with a two-element variable-power unit which permits variation in the total distance between the object and image planes with maintained aberration correction.

in the system according to the invention larger tolerances are permitted in the anastigmatic lens unit than would be permissible in the absence of the variable-power unit. When the system is installed in an apparatus such as a copier, any significant departure of the distance between the object and image planes, which will be referred to herein as the track length, resulting from the aggregate of the tolerance variations in the anastigmatic unit, can be corrected by means of the variable power unit.

Preferably the range of variation of the total distance between the object and image planes, or track length, is between 3.95 F and 4.15 F, where F is the equivalent focal length of the system for an infinity conjugate.

The system is preferably corrected to operate at a maximum relative aperture off/4.7. Although the system is particularly useful for application to the document-copying field, it is not restricted in its application to this field.

The anustigmatic lens unit preferably has substantially equal air separations. A variable-aperture device such as a mechanienl illH nuiy be included in the unnstlgmutlt' lens unit. in n preferred emlmdiment oithe invention the vurinhleuiperture device is positioned asymmetrically with respect to the number of lens elements in the anastigmatic unit, the variablepower unit being disposed on the side of the anastigmatic unit which is closer to the variable-aperture device.

Lens systems in accordance with the invention can be designed to give unit magnification over a wide semifield angle of, for example, 35.

In one embodiment of the invention the variable-power unit comprises a planoconvex lens element which is fixed relative to the anastigmatic lens unit and a planoconcave lens element which is adjustable in position relative to the fixed element to vary the power of said variable-power unit.

The anastigmatic lens unit may have different forms: for example said lens unit may comprise three or five lens elements including a central negative lens element, or may comprise four lens elements.

BRlEF DESCRlPTlON OF THE DRAWINGS The FZGURE is, by way of example, a diagrammatic partially sectioned elevation of a lens system according to the invention.

DESCRlPTiON OF THE PREFERRED EMBODKMENT The lens system illustrated comprises a symmetrical fiveelement anastigmatic lens unit ll of known type in combination with a twoelement variable power unit 2. As illustrated,

the object plane of the system is to the left of the system and the image plane to the right. The seven lens elements are numbered consecutively L -L from left to right, so that the variable-power unit comprises planoconcave and planoconvex lens elements L L respectively and the anastigmatic unit comprises elements Is -L the unit 2 being in this case disposed in front of the unit 1.

The five elements lu -L of the anastigmatic unit 1 and the rear element L of the variable-power unit 2. are mounted in fixed relative positions in a tubular lens mount 3, using conventional spacer rings to give the required spacing between the elements. The front element L of the variable-power unit 2 is mounted in a tubular support 4 which is in screw-threaded engagement with one end of the mount 3. Rotation of the support ll relative to the mount 3 is therefore effective to vary the separation of the elements L and L and thereby the power of the unit 2.

The five lens elements le -L of the anastigmatic unit l are symmetrical, that is to say, the elements L and L, are identical, and the elements L and L are identical, and the central element L is symmetrical. In the illustrated embodiment the elements L L, are collective and form respective doublets with the elements L.,, L,,, which are dispersive; the central element L is dispersive and is separated from the two doublets L L and L L, by respective airgaps 5 and 6 which in this case are unequal, the gap 5 being larger than the gap 6.

A variable aperture device in the form of a mechanical iris diaphragm 7 controlled by a lever 70 is mounted in the airgap 5 which is nearer the variable-power unit 2. By positioning the iris 7 in the gap 5 closer to the unit 2, asymmetry of the oblique aberrations of astigmatism, distortion, coma and oblique chromatic aberration caused by the variable-power unit 2 can be corrected.

Adjustment of the separation of the elements L,, L of the variable-power unit 2 by relative rotation of the mount 3 and support 4, as described previously, causes variation of the track length of the system. The track length of the system can therefore be adjusted to a given fixed value when the system is installed in apparatus such as, for example, a document copier. The presence of the variable-power unit 2 therefore permits a greater tolerance for the dimensions of the elements of the anastigmatic unit ll than would otherwise be acceptable. Consequently manufacture can be cheapened. The system is also such that advantage can be taken of simple and hence inexpensive types ofoptical glass for the lens elements.

The variable-power unit 2 in this embodiment is arranged to give u rnnge of vuriution ol' the truck length 'l of the system, while maintaining aberration correction, of 3.95 F to 4. l 5 F, where F is the equivalent focal length of the system for an infinity conjugate.

Numerical data relating to one example of a system as illustrated in the drawing are given below in Table l. Radii of curvature (R), lens thicknesses (d) and separations (S) are numbered consecutively from left to right of the drawing; radii of curvature are given as positive or negative according as the surfaces in question are convex or concave towards the object plane (i.e. towards the left of the drawing). The Table also gives the refractive index N,, for the sodium d-line and the Abbe V-number (V) for each lens element L L;.

Other data relating to this lens system are as follows:

Magnification 1:1

Equivalent focal length F Focal lengths of component lens elements:

Nominal track length T 4.0617 F Minimum track length 4.05 F

Maximum track length 4.074 F Maximumfnumber=f/4.7 Position oflris 7 0.0135 F behind L The following ranges for various parameters of the system have been found to give the most satisfactory results:

1. R! should be numerically equal to R3 and lie between 2.5

TAB LE I Lens .1. ad 11 T1 utclzuess Separation N11 S =Z.5780 Air R +371A350 L2.. rlz=2.5400 Ng=1.5181).l

S2 =0.6350 Air R5, -l-34.21)0O L3 (l3=5.7855 N3=L6204U Ra 29.7 180 L4 d4=1.0330 N;=1.53033 S3=3.8650 Air Rs 34.2JO0 L d 1.6865 N5 1.53033 S4=3.5225 Air R -242.3U45 L d1; =1.6330 N5 1.53033 R11: +2l).7180 L1 d1=5.7B55 N1=1.(5204O *8; variable from 0.5055 to 4.4680.

F and 5 F, wherein lenses L and L form the variable power unit and the 2. S3 and S4 should be between 0.03 F and 0.045 F, lenses L to L form the anastigmatic unit, R1 to R10 3. R5, R8, R9, R12 should preferably be equal and lie represent the radii of curvature of the lens surfaces from lens between 0.3 F and 0.4 F, L to lens L respectively, N1 to N7 represent the refractive in- 4. R7, R10 should preferably be equal and lie between 2 F dices of the lenses 1. to L respectively for the sodium d-line, and 3 F, V to V represent the Abbe V number for the lenses L to L 5. R6, R1 1 should preferably be equal and lie between 0.25 respectively, and S1 to S4 are the separations between lenses F and 0,35 F, L and L L and L L and L and L and 1.,; respectively. 6. The track length T should be variable between 3.95 F and An Optical lens System comprising a flve elemem anustig 415 matic lens unit in combination with a two-element variable 31 Should be vanable between 9 Fand power unit which permits variation in the total distance The Parameters of the glass employed the Vanous lens 35 between the object and image planes with maintained aberraments preferably lie in the following ranges of values: tion Con-action whergin i. N4=N5=N6 and lies between 1.50 and 1.55 ii. N3=N7 and lies between 1.60 and 1.65 a. lenses L and L form the variable power unit and lenses iii. N l=N2 and lies between 1.475 and 1.60 L to L form the anastigmatic unit,

iv. V4=V5=V6 and lies between 45 and 55 b. R1 to R12 represent the radii of curvature of the lens surv. V3=V7 and lies between 55 and 65 faces from lens L to lens L respectively, vi. V l=V2 and lies between 55 and 65 c. R2 equals R4 and both are infinite, vii. (N2-N4) and (N7-N6) lie between 0.075 and 0.15 d. R3 equals minus R1 viii. (V3-V4) and (V7-V6) lie between 7.5 and 12.5. e. The ratio of R5 to R1 is 34.290O to 371.4350 We claim: f. the ratio ofR6 to R1 is 29.7180 to 371.4350 1. An optical lens system comprising a five-element anastiggthe ratio f R R1 i 242-3945 I0 371-4350, matic lens unit in combination with a two-element variable h. R8 equals -R power unit which permits variation in the total distance R9 equals between the object and image planes with maintained aberra- 1- R10 equals minus tion correction, the various elements have numerical values R1 1 q s tm R substantially as follows: 1. R12 equals minus R5 Refractive Abbe Lens Radii Thickness Separation inIdIex, nutri ber,

R1: 371.4350 L1 R (l1=1.0050 Nt=l.51899 V1=60.42

P s1* Air R3=+371A350 L: R rlz=2.5400 N3=1-51899 Vg=60.4'2 s2=0.s35o Air R5=-|-34.2900 L3 d3=5.7855 Ns=1.62040 V3=602U Ra=29.7180 L1. zl;=1.6330 Nt=1.53033 V4:5l.10

S3=3.8650 Air 1 R 31.."J00 In. 415=L0805 N5=1.53033 V5=5L11l H al-31.21101) S-i=3.5225 All R101: 242.3t\45 L5 1I\-,=1.0330 Nn=1.53033 Vu=51.1.l

R =+2$LTl8O L7 (l =5.7855 N7=1.(i2040 V =00.21l

R13: -3-1.Z1l00 Variable from 0.5055 to 4.4680.

m. the thickness of the lenses L, to L are respectively d1 to I :17 where the ratio ofdl to R1 is 1.9050 to 371.4350, the ratio of d2 to dl is 2.5400 to 1.9050, the ratio d3 to dl is 5.7855 to 1.9050, the ratio d4 to dl is 1.6330 to 1.9050,

0.6350 to 371.4350, the ratio 5,, to S is 3.8650 to 0.6350, and the ratio S, to S is 3.5225 to 0.6350

o. the refractive indices of the lens L, to L for the sodium dline are N, to N, respectively where N, equals 1.51899, N equals N,, N, equals 1.62040, N, equals 1.53033, N, equals N,, N, equals N and N equals N and p. the Abbe V numbers of the lenses L, to L, are respectively V, to V, where V, equals 60.42, V, equals V,, V equals 60.29, V, equals 51.19, V equals V,, V,, equals V, and V, equals V 

1. An optical lens system comprising a five-element anastigmatic lens unit in combination with a two-element variable power unit which permits variation in the total distance between the object and image planes with maintained aberration correction, the various elements have numerical values substantially as follows:
 2. An optical lens system comprising a five-element anastigmatic lens unit in combination with a two-element variable power unit which permits variation in the total distance between the object and image planes with maintained aberration correction, wherein a. lenses L1 and L2 form the variable power unit and lenses L3 to L7 form the anastigmatic unit, b. R1 to R12 represent the radii of curvature of the lens surfaces from lens L1 to lens L7 respectively, c. R2 equals R4 and both are infinite, d. R3 equals minus R1 e. The ratio of R5 to R1 is -34.2900 to 371.4350 f. the ratio of R6 to R1 is 29.7180 to 371.4350 g. the ratio of R7 to R1 is -242.3945 to 371.4350, h. R8 equals -R5, i. R9 equals R5, j. R10 equals minus R7, k. R11 equals minus R6 l. R12 equals minus R5 m. the thickness of the lenses L1 to L7 are respectively d1 to d7 where the ratio of d1 to R1 is 1.9050 to 371.4350, the ratio of d2 to d1 is 2.5400 to 1.9050, the ratio d3 to d1 is 5.7855 to 1.9050, the ratio d4 to d1 is 1.6330 to 1.9050, the ratio d5 to d1 is 1.6865 to 1.9050, d6 equals d4, and d7 equals d3, n. the separation between lenses L1 and L2, L2 and L3, L4 and L5, and L6 and L7 are respectively S1, S2, S3 and S4 where the ratio S1 to R1 is variable from 0.5055 to 371.4350, to 4.4680 to 371.4350, the ratio S2 to R1 is 0.6350 to 371.4350, the ratio S3 to S2 is 3.8650 to 0.6350, and the ratio S4 to S2 is 3.5225 to 0.6350 o. the refractive indices of the lens L1 to L7 for the sodium d-line are N1 to N7 respectively where N1 equals 1.51899, N2 equals N1, N3 equals 1.62040, N4 equals 1.53033, N5 equals N4, N6 equals N4, and N7 equals N3, and p. the Abbe V numbers of the lenses L1 to L7 are respectively V1 to V7 where V1 equals 60.42, V2 equals V1, V3 equals 60.29, V4 equals 51.19, V5 equals V4, V6 equals V4 and V7 equals V3. 